When the resin currently used on an injection molding machine is to be changed to a new resin of a different kind or color, a resin part remaining within nozzle of the injection molding machine is discharged in preparation for the charging with the new resin. Such resin-discharging operation is called “purging”. Since the purging is performed while the nozzle is separated from a mold sprue, the resin while being still hot is allowed to scatter as it is purged from the nozzle. The scattering resin may burn or injure a human operator. The scatting resin may further damage a cylinder which is disposed near the nozzle for reciprocating an injection device or unit including the nozzle.
To deal with this problem, various purge shields have been proposed theretofore. One example of such purge shields is disclosed in Japanese Patent Application Laid-open Publication (JP-A) No. H05-309694. The disclosed purge shield is attached to a front plate (corresponding to a fixed platen) of an injection molding machine so as to prevent a resin from scattering as it is purged from a nozzle. The purge shield includes an inverted U-shaped attachment plate removably attached to a pair of laterally spaced L-shaped hooks fixedly provided on a front surface of the front plate, a horizontal top plate extending from an upper edge of the attachment plate in a direction away from the front plate, and vertical left and right side plates hinged to left and right edges, respectively, of the attachment plate for undergoing pivotal movement in a horizontal plane.
The purge shield of the foregoing construction is hooked on the L-shaped hooks and, hence, is readily removable from the front plate as a whole. In a state that the purge shield is attached to the front plate, the purge shield can be opened by simply turning the left side plate or the right side plate about its associated hinges through an angle of 90 degrees. A human operator is therefore allowed to perform visual confirmation of a state of engagement between the nozzle and a mold sprue.
The injection molding machine shown in JP H05-309694A is provided with a single cylinder disposed below the nozzle and extending along a longitudinal centerline of a base for reciprocating an injection unit. The single cylinder is likely to undergo slight lateral deflection as it is operating to reciprocate the injection unit. Since the lateral deflection directly affects the state of engagement between the nozzle and the mold sprue, an appropriate countermeasure is needed.
As one possible countermeasure, it may be considered that the single cylinder is replaced by two cylinders arranged such that a first cylinder is disposed on a lateral outer side of the left side plate of the purge shield, and a second cylinder is disposed on a lateral outer side of the right side plate of the purge shield. This arrangement, however, makes it impossible to place the purge shield in a fully-opened position due to interference between the side plates and the adjacent cylinders. To avoid this problem, the side plates should have a vertical length reduced so as to clear the cylinders. However, the side plates having a reduced vertical length can only achieve a limited purged-resin-scattering preventive function.
The demand for precision injection molding has increased in recent years. In view of this, it is desirable that a purge shield has side plates which can be easily opened and closed even when the purge shield is used with an injection molding machine having two cylinders for reciprocating an injection unit.
It is accordingly an object of the present invention to provide an injection molding machine equipped with a purge shield having a side plate that can be opened and closed with utmost ease.